Drink bottled water when traveling and make sure you or the waiter opens the bottle in front of you. In some places, some restaurants refill the bottles and use tap water which can make you sick. If the quality of the water is really questionable, order sparking water because you can hear the fizz when the bottle is opened or if the sparkling water is flat you will know that it has been open for a while.
Be careful of the ice in beverages - especially in third world countries. Not very many hotels or restaurants filter the ice that they use to serve drinks, so be careful not to order your drinks containing ice when traveling.